Liverpool are top of the Premier League table at Christmas. On the face of it, that's no great surprise considering the comprehensive manner of their title triumph last season, which saw Jurgen Klopp's side crowned champions with an 18-point margin over runners-up Manchester City, but securing the Christmas No. 1 spot this time around is a bigger achievement that it initially appears.

It hasn't all been plain sailing to the top, as first-choice defensive pairing Virgil van Dijk and Joe Gomez have been ruled out for months with serious knee injuries and a succession of first-team regulars were sidelined following positive COVID-19 tests. New signings Thiago Alcantara and Diogo Jota also have been hit by injuries, and there was the unforgettable 7-2 defeat at Aston Villa in October -- the heaviest loss suffered by any reigning Premier League champion -- that hinted at problems ahead.

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Despite these bumps in the road, Liverpool are four points clear at the top and strong favourites to retain the title, just a year after winning it for the first time since 1990. They have, so far, overcome all of the challenges that had threatened to derail the defence of their title, and the failure of any of their challengers to build a convincing argument of their ability to last the pace makes it difficult to foresee anything other than Liverpool crowned champions again in May.

Liverpool are looking ominous, and it's perhaps time to suggest that Klopp's team is on course to become one of the Premier League greats, not because of their successes, but because of the way they have dealt with the setbacks to maintain their position at the top.

Klopp's team are unquestionably the dominant force in English football right now. Champions League winners in 2019 -- a year after being beaten finalists against Real Madrid in Kiev -- and Premier League champions in 2020, plus the UEFA Super Cup and FIFA Club World Cup winners last season, this Liverpool side has won the biggest trophies and overhauled Pep Guardiola's record-breaking Manchester City side.

At times during that charge to the top, it became a straightforward exercise to predict Klopp's team. They rarely suffered injuries or suspensions; in a sense, consistency became the team's 12th man. But that has changed this season and the loss of Van Dijk in October, when the Dutch defender suffered a cruciate ligament injury during the 2-2 draw at Everton, looked like being a hammer blow. After all, Liverpool's rise could be virtually traced back to Van Dijk's arrival from Southampton in January 2018, so how would they cope without his authority and leadership at the back?

When Gomez then injured a knee tendon on England duty in November, it compounded the loss of Van Dijk. All of a sudden, Klopp was faced with being without his two best centre-halves, potentially for the rest of the season. But Liverpool have lost just once in 15 games since Van Dijk's injury -- a Champions League defeat against Atalanta, a game in which Klopp made wholesale changes -- and the likes of Nat Phillips and Rhys Williams have stepped up alongside Joel Matip, along with makeshift centre-half Fabinho, to enable the team to remain on course.

It's been a similar story in midfield. Thiago has started just one Premier League game since his summer arrival from Bayern Munich, and Alex Oxlade-Chamberlain's cameo against Crystal Palace on Saturday was his first appearance of the 2020-21 season. Fabinho has been forced to drop into defence and captain Jordan Henderson also spent a month on the sidelines. But Georginio Wijnaldum has filled the gaps in every league game and 19-year-old Curtis Jones has shown himself to be a star of the future in recent weeks, producing a series of outstanding performances while deputising for his more experienced teammates.

In attack, Jota made an instant impact following his summer switch from Wolves, with nine goals in all competitions before suffering a knee injury earlier this month -- his contributions kept Liverpool on track while Sadio Mane and Roberto Firmino struggled for early-season goals.

Every issue that Liverpool and Klopp have had to address this season has been solved by the performances of squad players who had perhaps been underestimated prior to the campaign. Whenever the Reds' fringe players have been drafted in, they have performed so well that the more established stars haven't been missed, which is why Liverpool are now such a force to be reckoned with.

Liverpool's depth is unmatched in the Premier League and they have the winning mentality and experience to go with it, so they will take some shifting from the position they now find themselves in at the top of the Premier League. Still, it must be stressed that Christmas has come early this season -- literally -- with the delayed start to the campaign ensuring that most teams have played four fewer games than they would ordinarily have amassed by this stage.

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Twelve months ago, Liverpool were 10 points clear of second-placed Leicester, having played one game fewer than Brendan Rodgers' side, and they are threatening to pull away again. Nine times in the past 12 seasons, the leaders at Christmas have gone on to win the Premier League. Liverpool had been the side to let it slip on those three occasions when it didn't happen, but they didn't falter last season and remained top all the way until the end of the pandemic-interrupted campaign.

Who can realistically stop them this time? Leicester are second again at Christmas, but they tailed off dramatically last season, while Manchester United are resurgent, though unlikely to emerge as serious contenders to win the league in 2021. Spurs and Chelsea have seen good starts evaporate, with both now outside the top four, while City appear to have lost their impetus and desire under Guardiola.

Liverpool have had to deal with plenty of roadblocks this season, but they have found a way past all of them. The biggest concern for the chasing pack heading into the new year is that they only appear to be getting better and stronger.